Memory functionality is a prerequisite for many electronic applications in modern society. In fact, most envisioned electronic applications require non-volatile memory systems that can be programmed, erased and read-out electrically. One of the strongest trends in modern technology today is to embed and integrate printed electronic systems of various kinds into various low-cost items, such as packages, tags and stickers, for applications in distributed diagnostics, track-and-trace, safety and much more. Organic non-volatile memory devices based on ferroelectricity represent a promising approach towards the development of a low-cost technology that is possible to manufacture using common printing technologies (Scott et al., “Nonvolatile memory elements based on organic materials”, Advanced Materials 19, 1452-1463 (2007)).
Transistors are extensively used in conventional semiconductor memories. Organic ferroelectric field-effect transistors are ideally suited for the achievement of low-cost, high-performance non-volatile memory technology, as they allow for long data retention time and non-destructive read-out voltage typically of around 2-4 V. The latter arises from the high charge carrier concentration induced in the semiconductor by the ferroelectric polarization of the gate insulator, which provides resistive switching between a high (on-state) or low (off-state) drain current level. The read-out operation requires a source-drain bias that is of the same order of magnitude as that of the writing voltage that is achieved by addressing the gate. This means that the read-out operation can potentially disturb the polarization of these ferroelectric field-effect transistor cells.
Therefore, there is a desire to develop a ferroelectric gate insulator material system that provides high charge carrier concentrations in the organic semiconductor already at drain-source voltages far below the voltage needed to switch the ferroelectric field-effect transistor cell via the gate.